For a rubber article such as a tire, a steel cord formed by twisting a plurality of steel filaments is widely used as a reinforcing material. In particular, since a tire used for a heavy duty vehicle such as a construction vehicle is used under heavy loading on rough terrain having sharp rises or drops or the like, a steel cord to be used as a reinforcing material is demanded to have a particularly high strength and resistance. For this reason, in such a large tire, a steel cord having a so-called multi-twisted structure, which is formed by twisting a plurality of strands formed by twisting a plurality of steel filaments, is employed.
As a prior art relating to a steel cord having a multi-twisted structure, for example, Patent Document 1 discloses a steel cord constituted in such a manner that, in order to surely allow rubber penetrate to the inside of the cord having a multi-twisted structure, around one core strand composed of a plurality of filaments, five sheath strands having the same diameter as that of the core strand, each composed of a plurality of filaments, are twisted.